Conventionally, measurement of the fuel volume in a fuel tank of a fuel cell is estimated by a fuel surface height of the fuel, which can be obtained by the upper liquid level and the lower liquid level. However, the liquid level in the fuel tank is generally not in a simple equal level and may be variable with correspondence to the usage of the fuel. Thus, inaccuracy occurs in the measurement of the fuel volume, creating a negative effect for the performance of the fuel cell.
Accordingly, the invention utilizes the capacitance theory to maintain the fluid in the fuel tank in a stable form effectively for measurement of the fuel volume, thus enhancing the accuracy of the measurement while reducing the manufacturing cost.